Electromagnetic relay with adjustable magnetic shunt



F. 0.-' SMELTZ Filed Jan. 4, 1952 ELECTROMAGNETIC RELAY WITH ADJUSTABLEMAGNETIC SHUNT faIuIIFIIII May 11, 1954 im Il AMW Patented May 11, 1954ELECTROMAGNETIC RELAY WITH ADJUST- ABLE MAGNETIC SHUNT Floyd O. Smeltz,Milwaukee, Wis., assignor to Allis-Chalmers Manufacturing Company,Milwaukee, Wis.

Application J anuary-4, 1952, Serial No. 264,886

6 Claims.

This invention relates in general to electromagnetic relays and inparticular to electromagnetic relays utilizing magnetic shunts.

It is well known inA electromagnetic relays to utilize an adjustablemagnetic member in shunt with the magnetic Working gap for the purposeof causing' the relay to operate or trip at any prescribed value ofmagnetomotive force within the adjusting range of the relay. However,magnetic shunts differ in physical construction and method of reluctanceadjustment. Ordinarily reluctance adjustment of the shunt isaccomplished by changing the length of an included shunt magnetic airgap. In simple form such shunts comprise a magnetic member having aplane surface movable in av direction which is essentially parallel tothe direction of shunted flux. That is, the shunting member is movabletoward or away from a pole piece of the relay. Such construction has thedisadvantage that the neness of adjustment obtainable is very limited,

since if the shunting member is quite distant from the pole piece withrespect tothe shunted member, the position of the shunting member iswithout appericable effect on the division of uX between the shuntingmember and shunted'member. Conversely, if the shunting member is quiteclose to the pole piece with respect to the position of the shuntedmember, a small change in the position of the shunting member produces avery large change in the division of flux between the shunting memberand shunted member. This results generally in insensitive control and anundesirable, nonlinear relationship between the travel of the shuntingmember and the total actuating magnetomotive force, thereby renderingcalibration of the relay difcult.

lThis disadvantage may be overcome by utilizing a relay in which themagnetic shunt comprises a member of adjustable magnetic cross sectionnormal to the direction of shunted flux. Such a magnetic shunt dependsupon the saturation of the member of adjustablel cross section tocontrol the division of flux between the shunting and shunted members.Such a magnetic shunt in addition, may utilize an included, adjustablemagnetic air gap to aid in controlling the division of ux between theshunting and shunted members. Thus, a relay may be utilizedwhich-comprises a magnetic shunt providing a very. wide range ofreluctance adjustment relative to the reluctance of the shunted member,providing a very precise control of shunt'reluctance and thus a. precisecontrol over total relay actuating magnetomotive force, and having anadjustment characteristic which is substantiallylinear.

to provide an electromagnetic relay having an adjustable magnetic shuntwhich provides for a high sensitivity of adjustment over a very widerange of total adjustment.

It is an additional object of this invention to l provide an improvedelectromagnetic relay having an adjustable magnetic shunt provided withindicating means for indicating an operating characteristic of therelay.

Objects and advantages other than those set forth above will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. 1 is a side elevation, partly in section, of one embodiment of theinvention utilizing an electromagnetic biasing coil in -the mainmagnetic path;

Fig. 2 is a front view of the relay shown in Fig. l with a portion ofthe contact cover broken away;

Fig. 3 is a plan view of a portion of the relay illustrating theindicating device;

Fig. 4 is an enlarged side view of a the adjustable magnetic shunt;

Fig. 5 is a vertical section taken along the line V-V of Fig. 4

Fig. 6 is a side elevation of an alternate embodiment of the inventionutilizing an electromagnetic biasing coil in a shunted magnetic path;and

Fig. 7 is a view of a portion of an additional alternate embodimentV ofthe invention utilizing an included shunt air gap.

Referring more particularly to the drawing by character of reference,the preferred embodiment of the invention illustrated in Figs. l to 5",comprises a U-shaped'magnetic yoke 'i having two spaced legs ii, 9 and abase member H. The yoke i is held't'ogether by suitable screws l2.Extending acrossthe'upper ends of legs 8,' 9 is a magnetic bridlngmember i3 comprising a pair of magnetic'members I4', lsecured to legst?, respectively, and separated lby 'an air gap I6 (Fig. 3). v Suitable'adjustable. magnetic means are proportion of Y vided to vary thereluctance ofhthe magnetic path including member I4 and a portion ofmember I5 to vary operating characteristics of the relay, and such meansmay comprise a magnetic screw I1. If screw I1 is utilized, the end ofmembers I4, I5 adjacent air gap I6 are tapped to provide a tappedopening in which screw I1 moves to vary the reluctance between magneticmembers I4 and I5. Screw I1 may be provided with a lock nut IS toprevent undesired movement of the screw. If additional rigidity ofmembers I4, I5 is desired, pieces or blocks I9 of suitable nonmagneticmaterial, such as brass, may be secured to the ends of members I4, I5adjacent air gap I6 by any suitable means such as resistance welding.Blocks I9 are preferably tapped in conjunction with members I4, I5 toprovide tapped top and bottom walls for the tapped opening betweenmembers I4, I5.

A suitable calibrated scale 2| is associated with screw I1 to indicatevariations in an operating characteristic of the relay in dependenceupon the position of screw I1. As shown, scale 2| is secured to memberI4 by a screw 22 and is calibrated in terms of the current required tooperate the relay.

The relay further comprises an armature 25 having one end thereofdisposed adjacent to, and attractable toward, the pole piece formed byan extension piece I mounted on bridging member I3 in alignment with leg8. Suitable pivot means are provided to pivotally support armature 25,and such means may comprise a knife edge member 25 secured to member I5between core leg 9 and magnetic screw I1. A support member 28 ofnonmagnetic material is secured to member I through a nonmagnetic spacerby screws 29 and is secured to leg 8 by suitable means (not shown) toprovide support for a terminal board 3|. Terminal board 3| is secured tosupport member 28 by bolts 32 and nuts 33 and is provided with at leasttwo stationary terminal studs 34 to be connected to a circuit to becontrolled and having at the lower ends thereof xed contacts 35.

Contacts 35 are adapted to engage a pair of movable contacts 36 carriedby a exible conducting member 31 secured to the end of armature by ascrew 38 and an insulating support member 38. 'I'he fixed and movablecontact assemblies may be enclosed in any suitable dust tight member,such as a transparent cover 4| secured to terminal board 3|. A stud 42having a spring 43 compressed between board 3| and an adjusting nut 44extends loosely through terminal board 3| and is secured to armature 25to control the pickup characteristics of the relay. A

similar stud 45 having a spring 4S compressed between armature 25 and anadjusting nut 41 ex tends loosely through an opening in armature 25 andis secured to terminal board 3| to control the drop-out characteristicsof the relay. When the armature 25 is not attracted toward extensionIIJ, spring 46 is not compressed, so that only spring 43 holds armature25 in the deenergized position. When armature 25 is attracted toward thepole piece formed by extension II), spring 46 is compressed so that theforce of this spring is added to the force exerted by spring 43 toproduce the desired combined spring characteristic.

The relay may be mounted in any suitable manner, and if the relay is tobe utilized as a through conductor relay, a mounting bracket 5| securedto core leg 9 by screws 52 may be provided. Bracket 5| is secured to aconductor or conductors, represented by bus bar sections 53, by aninsulated bolt 54. Bus bar sections 53 provide parallel paths for thecurrent which it is desired to control and represent energizing meansfor producing flux in the relay core. If desired, an electromagneticcoil 56 may be provided on the relay core to produce a biasingmagnetomotive force in addition to the magnetomotive force produced bythe current in bus sections 53.

In operation as a through current relay, the relay is secured to bussections 53 which carry the current to be controlled. The flux producedin the relay travels through leg 9, member II and leg 8 and then comesto a junction providing two parallel magnetic paths. The first such pathincludes the extension I0 of leg 8, the working air gap between thisextension and armature 25, armature 25 and pivot means 26 to member I5.The second magnetic path includes the adjustable magnetic shunt andcomprises member I4, the air gap I6 and screw I1 between members I4 andI5 to member I5.

The division of flux between these two magnetic paths depends upon therelative permeances of the paths, and by adjusting the position of screwI1 in the air gap, the permeance of the second magnetic path may bevaried over a wide range. As screw I1 is advanced in the threadedopening, the permeance of the second path is increased to increase theflux in the second path. Thus, by adjustment of screw I1, the current inbus sections 53 or coil 56 at which armature 25 is attracted toward leg8 is varied to produce operation of the relay at any desired value ofmagnetomotive force. Screw I1 advances in a direction transverse to thedirection of flux in members I4 and I5 increasing the effective crosssectional area of the magnetic path across air gap I6 so that thepermeance of the shunt path varies substantially linearly with respectto the advance of screw I1. Thus a substantially linear relationshipexists between the travel of the screw |1 and the net magnetomotiveforce acting upon the relay core at which armature 25 is attracted. Theportion of the screw I1 which is engaged in the air gap I6 forms thesaturable section of variable cross section mentioned above.

Fig. 6 illustrates an alternate embodiment of the invention in whichcoil 56 of Fig. l has been replaced or supplemented by a coil 6I)encircling pivot means 26. Pivot means 26 and extension 1|0 have beenincreased in length so as to accommodate coil `6D between armature 25and member I3.

The effect on the relay shown in 6 of a given number of ampere turns incoil 60 is greater than the effect of the same number of ampere turns inbus sections 53 or of coil 56 in Fig. l, since in'Fig. 6 coil G5 is inthe working magnetic circuit which is traversed by only a portion of theflux produced by the current in bus sections 53 or coil 58. The relayshown in Fig. 6 will trip at a number of ampere turns in coil B0 whichis substantially independent of the position of screw I1 and which isalways equal to or less than the number of ampere turns in coil 5S orbus sections 53 at which the relay is tripped.

It will be obvious that by suitable modifications, coil 60 may bedisposed in other suitable locations in the working magnetic path, suchas on extension I0 or around `armature 25.

Fig. 7 illustrates an additional alternate ernbodiment of the inventionin which a piece or insert 6I of suitable nonmagnetic material, such asbrass, is provided in a portion of the edge of member I4 adjacent airgap I6 and adjacent to the unadvanced position of screw I1. Insert 6|'is utilized when it is desiredto employY adjustment of an includedshunt Vair gap in addition to adjustment of a. magnetic cross section ofa portion of the shunt path. Since screw Il must be adparting from-thespirit of the invention or from the scope of the appended claims.

It is claimed and desired A`to secure by Letters Patent:

1. An electromagnetic relay comprising a U-shaped magnetic core havingrst and second legs denning a passage for the insertion of a 4currentcarrying conductor, a magnetic bridging 'member secured across saidcorelegs, a magnetic armature having one end thereof disposed adjacentto said first core leg, pivot means for pivotally mounting said armatureon said bridging member, said armature and said pivot means forming arst magnetic path, the portion of said bridging member disposed betweensaid first core leg and said pivot means forming a second magnetic pathin parallel with said rst path, and adjustable magnetic means in saidbridging member for varying the magnetic reluctance of said secondmagnetic path to vary the division of flux between said first and secondmagnetic paths.

2. An electromagnetic relay comprising a U-shaped magnetic core havingfirst and second legs defining a passage for the insertion of a currentcarrying conductor, a magnetic` bridging member secured across said corelegs, a magnetic armature having one end thereof disposed adjacent tosaid rst core leg, pivot means for pivotally mounting the other end ofsaid armature on said bridging member, said armature and said pivotmeans forming a rst magnetic path, the portion of said bridging memberdisposed between said rst core leg and said pivot means forming a secondmagnetic path in parallel with said first path, adjustable magneticmeans in said bridging member for varying the magnetic U reluctance ofsaid second magnetic path to vary the division of ilu-X between saidfirst and second magnetic paths, and a calibrated scale associated withsaid magnetic means for indicating variations in an operatingcharacteristic of said relay in dependence upon the position of saidadjustable magnetic means.

3. An electromagnetic relay comprising a U-shaped magnetic core havingfirst and second legs defining a passage for the insertion of a currentcarrying conductor, a magnetic bridging member secured across said corelegs, said bridging member comprising a pair of magnetic membersseparated by an air gap, the ends of said members adjacent said air gaphaving tapped surfaces to provide a tapped opening, a magnetic armaturehaving one end thereof disposed adjacent to said rst core leg, pivotmeans disposed on said bridging member between said second core leg andsaid opening for pivotally mounting the other end of said armature, saidarmature and said pivot means forming a nrst magnetic path, the portionof said bridging member disposed betweensaid first core leg and saidpivot means forming a second magnetic path in paralle] with said rstpath, and a magneticferrous threadedimember engaged in saidtappedopening Vto vary the effective cross sectional area of the ferrousmagnetic path provided by said threaded member, whereby movement of saidthreaded membervaries the permeance of said second magnetic path to varythe division of fiux between said rst and second magnetic paths.

4. An electromagnetic relay comprising a U- shaped magnetic core having'irst and second legs defining a passage for the insertion of a currentcarrying conductor, a magnetic bridging member secured across said corelegs, said bridging membercomprising a pair of magnetic membersseparated by an air gap, the ends or said members `adjacent said air gaphaving tapped surfaces to provide a tapped opening, a 'inagneticarmature having one end thereof disposed adjacent to said first coreleg, pivot means disposed on said bridging member between saidsecondcore leg and said opening for pivotally mounting the other end of saidarmature, said armature and said pivot means `forming a first magneticpath, the portion of said bridging member disposed between said firstcore leg and said pivot means forming a second magnetic path in parallelwith said rst path, a ferrous threaded member engaged in said tappedopening to vary the effective cross sectional area of the ferrousmagnetic path provided by said threaded member in said air gap, wherebymovement of said threaded member varies the magnetic permeance of saidsecond magnetic path to vary the division of flux between said first andsecond magnetic paths, and a calibrated scale adjacent said threadedmember for indicating variations of an operating characteristic of saidrelay in dependence upon theposition of said threaded member.

5. An electromagnetic relay comprising a U- shaped magnetic core havingfirst and second legs defining a passage for the insertion of a currentcarrying conductor, a magnetic bridging member secured across said corelegs, said bridging member comprising a pair of magnetic membersseparated by an air gap, a pair of nonmagnetic blocks secured to theends of said magnetic members adjacent said air gap to secure saidmagnetic members together, the portions of said blocks adjacent said airgap and the ends or" said members adjacent said air gap having tappedsurfaces to provide a tapped opening, a magnetic armature having one endthereof disposed adjacent to said rst core leg, pivot means disposed onsaid bridging member between said second core leg and said opening forpivotally mounting the other end of said armature, said armature andsaid pivot means forming a first magnetic path, the portion of saidbridging member disposed between said first core leg and said pivotmeans forming a second magnetic path in parallel with said first path,and la ferrous threaded member engaged in said tapped opening to varythe effective cross sectional area of the ferrous magnetic path providedby said threaded member in said air gap, whereby movement of saidthreaded member varies the magnetic permeance of said second magneticpath to vary the division of flux between said rst and second magneticpaths.

6. An electromagnetic relay comprising a U- shaped magnetic core havingrst and second legs defining a passage for the insertion of a currentcarrying conductor, a magnetic bridging member secured across said corelegs, said bridging member comprising a pair of magnetic mem bersseparated by an air gap, a pair of nonmagnetic blocks secured to theends of said magnetic members adjacent said air gap to secure saidmagnetic members together, the portions of said blocks adjacent said airgap and the ends of said members adjacent said air gap having tappedsurfaces to provide a tapped opening, a magnetic armature having one endthereof disposed adjacent to said rst core leg, pivot means disposed onsaid bridging member between said second core leg and said opening forpivotally mounting the other end of said armature, said armature andsaid pivot means forming a rst magnetic path, the portion of saidbridging mern ber disposed between said rst core leg and said pivotmeans forming a second magnetic path in parallel with said rst path, aferrous threaded member engaged in said tapped opening to vary theeffective cross sectional area of the magnetic path provided by saidferrous member in said air gap, whereby movement of said ferrous membervaries the magnetic permeance of said second magnetic path to vary thedivision of flux between said first and second magnetic paths, and acalibrated scale adjacent said ferrous member for indicating variationsof an operating characteristic of said relay in dependence upon theposition of said ferrous member.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 265,485 Cochran Oct. 3, 1882 1,920,818 Verrall Aug. 1, 19332,179,305 Stickney et al. Nov. 7, 1939 2,282,933 Cahill May 12, 19422,442,016 Poole May 25, 1948 2,549,371 Fereday Apr. 17, 1951 FOREIGNPATENTS Number Country Date 585,629 France Dec. 12, 1924

